Medical imaging by nuclear magnetic resonance has progressively improved over the course of the last decade to an impressive degree. Concomitant with the spatial resolution achieved through the imaging procedure, there is a strong desire to practice noninvasive detailed analysis of the chemical nature of the subject matter imaged. The potential of NMR as an analytical tool for in vivo studies depends upon the ability to localize spectral data to a specific selected spatial volume. One of the approaches for such spatial localization is to shape the RF field produced by "depth pulses" applied from a pair of closely coupled RF coils disposed on the surface of the body under study. It is known to so arrange such coils, each comprising a tuned circuit, with circuit means to actively detune either said coil with respect to the other. In this prior art, each said coil is terminated in a .lambda./4 cable which is selectively open or shorted by a reed relay located outside the magnetic field of the instrument. See Bendall, et al., J. Mag. Res., V. 60, pp. 473-478 (1984).
In the prior art, effort has been directed toward rendering "invisible", one coil to the other, of a pair of closely disposed coils. Thus, prior art exploited active detuning schemes to reduce the effect of one inactive, but closely coupled coil, on the other, active coil. In some instances the two coils are respective portions of each of a transmit (RF source) circuit and a receive (RF sink) circuit. In other instances, both coils may serve as transmit circuit members, albeit at different times, their differing geometry providing an additional degree of freedom within a pulse sequence. Examples of these may be found in Edelstein, et al., J. Mag. Res., v. 67, pp. 156-161 (1986) and in Bendall, Chem. Phys. Lett., v. 99, p. 310 (1983).